1. Field of the Invention
The present invention relates to a control apparatus which is applied to hybrid vehicles which are provided with an internal combustion engine, a continuously variable transmission, and an electric motor, where the output shaft of the internal combustion engine is connected to the input side of the continuously variable transmission, the output side of the continuously variable transmission is connected to the output shaft of the electric motor via an engaging part comprising a pair of engaging elements which are freely engageable and disengageable, and the output shaft of the electric motor is connected to a drive force transmission device which is coupled with the drive wheels.
This application is based on Japanese Patent Application No. Hei 11-98210, the contents of which are incorporated herein by reference.
2. Description of the Related Art
The control apparatus described in Japanese Unexamined Patent Application, First Publication, No. Hei 9-224303 which is depicted in FIG. 4, for example, is known as a control apparatus for hybrid vehicles of this type. In FIG. 4, the output shaft of engine 1 drives oil pump 2, and is coupled with the input shaft of the continuously variable transmission 3, while the output shaft of an electric motor 6 is coupled with the output shaft of the continuously variable transmission 3 via a clutch 4 and a gear 5. Furthermore, the drive wheels 8 are coupled with the output shaft of the continuously variable transmission 3 via a differential gear 7.
Furthermore, a rotation sensor (not depicted in the figure) which detects rotational speed is attached to the output shaft of the continuously variable transmission 3, and the output signal from the rotation sensor is input into the input port of an electronic control unit (ECU) 9. Furthermore, the vehicle velocity is ascertained in ECU 9 from the reduction gear ratio of the differential gear 7 and the effective tire radius.
What is depicted in FIGS. 5 and 6 is the order of operation during vehicle running in this control apparatus for hybrid vehicles. By means of this, the control in the hybrid vehicle during start is as described hereinbelow. In other words, when the driver steps on the accelerator pedal, in step S101, the accelerator switch is determined to be ON and control proceeds to step S102. In step S102, if it is determined that the vehicle velocity V is equal to or below 10 km/h, then it is determined that torque cannot be smoothly generated by engine 1, and in step S301, the clutch 4 is opened, and in step S302, the engine 1 is maintained in an idling state, while in step S303, the vehicle runs solely using the torque of the electric motor 6. On the other hand, when it is determined in step S102 that the vehicle velocity V is above 10 km/h, then in step S103, the clutch 4 is placed in the engaged state. In this step S103, the clutch 4 is connected when the rotational speed of the input shaft of the continuously variable transmission 3 and the idling engine speed of engine 1 are in agreement.
By means of this control, during start, when the vehicle velocity V is equal to or below 10 km/h, then engine 1 is placed in an idling state, while when vehicle velocity V is in excess of 10 km/h, the clutch 4 is engaged when the rotational speed of the input shaft of the continuously variable transmission 3 and the idling engine speed of the engine 1 are in agreement. In this case, as shown in FIG. 4, the output shaft of the engine 1 and the input shaft of the continuously variable transmission 3 coincide, so that if the engine 1 is in an idling state, the rotational speed of the input shaft of the continuously variable transmission 3 must be in agreement with the idling engine speed. Accordingly, in such a hybrid vehicle, when the vehicle velocity V exceeds 10 km/h after start, the clutch 4 is connected, and at this point, the engine speed of the engine 1 is the idling engine speed.
However, in the hybrid vehicle described above, when the vehicle velocity is equal to or below a predetermined velocity (10 km/h), clutch 4 remains disengaged; however, when the vehicle velocity is in excess of a fixed value (10 km/h), then the engagement of clutch 4 is conducted while engine 1 is at the idling engine speed. For this reason, in cases when it is necessary to operate with a high engine output after the engagement of clutch 4, because the engine speed is near the idling engine speed, it is impossible to obtain sufficient output, or alternatively, operating with a high output is conducted while maintaining a low engine speed, so that there are large fluctuations in the torque of engine 1, resonance phenomena are induced in the drive system, and there is a possibility that the vehicle will lapse into the so-called xe2x80x9csurgingxe2x80x9d state.
In view of the above circumstances, the present invention has as an object thereof to provide a control apparatus for hybrid vehicle which makes it possible to effectively avoid the so-called surging phenomenon by preventing the engagement of the engaging part (clutch) under appropriate conditions.
In order to attain the object described above, the following compositions are adopted in the present invention.
That is to say, in a first aspect of the present invention, a control apparatus (for example, control apparatus 11 in the embodiments) applied to hybrid vehicles (for example, hybrid vehicle 10 in the embodiments) which are provided with an internal combustion engine (for example, engine E in the embodiments), a continuously variable transmission (for example, CVT 18 in the embodiments), and an electric motor (for example, drive/regeneration motor M in the embodiments), where an output shaft of the internal combustion engine is connected to an input side of the continuously variable transmission(for example, drive side pulley 19 in the embodiments), and an output side of the continuously variable transmission (for example, driven side pulley 21 in the embodiments) is connected to an output shaft of the electric motor via an engaging part (for example, clutch 28 in the embodiments), comprising a pair of engaging elements (for example, engaging elements 26 and 27 in the embodiments) which are freely engageable and disengageable, and the output shaft of the electric motor is connected to a drive force transmission device (for example, final reduction gear 30 in the embodiments) coupled to the drive wheels; wherein: an engaging element controller (for example, steps S7 and S9 in the embodiments), for controlling engagement and disengagement operations of the engaging elements, a rotational speed detector (for example, step S2 in the embodiments) for detecting the rotational speed of, among the engaging elements, at least that engaging element (for example, engaging element 27 in the embodiments) positioned at the output shaft side of the electric motor, a gear ratio detector (for example, step S3 in the embodiments) for detecting a gear ratio of the continuously variable transmission, and a gear ratio controller (for example, step S8 in the embodiments) for controlling the gear ratio of the continuously variable transmission, are provided. Additionally, control is conducted so that, when the product of the rotational speed of the engaging element positioned at the output shaft side of the electric motor and the gear ratio of the continuously variable transmission is equal to or below a predetermined value (for example, a threshold value in the embodiments (concretely, for example, 1000 rpm)), complete engagement of the engaging elements is prohibited, and the gear ratio is increased.
In the composition described above, when the engaging elements are completely engaged with one another, the product of the rotational speed of the engaging element positioned at the output shaft of the electric motor and the gear ratio of the continuously variable transmission is equal to the engine speed of the internal combustion engine. Here, in the composition described above, when this product is equal to or below a predetermined value, the complete engagement of the engaging elements with one another is prevented, and control is conducted such that the gear ratio of the continuously variable transmission becomes large. Accordingly, when the engaging elements are in a state of engagement with one another, and the engine speed of the internal combustion engine falls undesirably to or below a predetermined value, it is possible to open the engaging part, or to create a half engaged clutch state, to avoid a complete engagement of the engaging elements with one another. By means of this, the state does not result in which the internal combustion engine is connected to the drive system while at a low engine speed and has a high load placed thereon, and thus it is possible to effectively avoid the occurrence of the resonance phenomenon (surging) of the drive system resulting from increases in the fluctuation of the torque of the internal combustion engine. By means of this, it is possible to improve the optimum driving characteristics of the hybrid vehicle.
In a second aspect of the present invention, a required output calculator (for example, step S51 in the embodiments) for calculating output required of the internal combustion engine is provided, and as the calculated output increases in size, the predetermined value is set so as to be increased.
Since this composition is employed, in this hybrid vehicle, as the output required of the internal combustion engine increases, the predetermined value is set so as to be increased, so that as the output required of the internal combustion engine increases, it is not the case that the internal combustion engine is connected to the drive system in a state in which it has a low engine speed, and accordingly, it is possible to reliably avoid the state in which high output driving is conducted while the internal combustion engine has a low engine speed. By means of this, an effect is achieved whereby surging is effectively prevented.